Alloy for superconductive magnet

ABSTRACT

A ternary alloy, suitable for superconductive magnets, contains 30-90 atomic percent vanadium, 5-65 atomic percent hafnium, and less than 40 atomic percent niobium.

United States Patent Tachikawa et al.

[111 3,792,990 [451 Feb. 19, 1974 ALLOY FOR SUPERCONDUCTIV E MAGNET Inventors: Kyoji Tacliikawa; Kiyoshi Inoue, both of Tokyo, Japan Assignee: The Director of National Research Institute for Metals, Tokyo, Japan Filed: Nov. 28, 1972 App]. No.: 310,023

Foreign Application Priority Data Dec. 27, 197] Japan 46-105345 U.S. Cl. 75/134 V, 75/174 Int. Cl. C22c 27/00 Field of Search 75/134 V, 174

[56] References Cited UNITED STATES PATENTS 3,215,569 11/1965 Kneip et a1. 75/174 X 3,408,604 10/1968 Doi et al. 75/174 X 3,449,118 6/1969 Holtz 75/134 V 3,671,226 6/1972 Komata et al. 75/174 X Primary Examiner-L. Dewayne Rutledge Assistant ExaminerE. L. Weise Attorney, Agent, or FirmBrooks Haidt & Haffner [57] ABSTRACT A ternary alloy, suitable for superconductive magnets, contains 30-90 atomic percent vanadium, 5-65 atomic percent hafnium, and less than 40 atomic percent niobium.

1 Claim, 3 Drawing Figures NOT LESS THAN 9.5 "K

' PATENTEUFEBISIQM 3,792,990-

loo-20o KOe 2 K08 $211 ZE KOB PAIENIEDIFEBWW I 3.792.990

SHEET 7 3 BF 3 m. 3 id) ALLOY FOR SUPERCONDUCTIVE MAGNET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a novel alloy for superconductive magnet and more particularly, to a novel alloy for superconductive magnet compound of V, Hf and Nb.

2. Description of the Prior Art Heretofore, there have been known alloys of niobium base and vanadium base. Among them, Nb-Ti alloy, Nb-Zr alloy and V-Ti alloy show critical temperature as high as 8-l0K.

As ternary alloy, there are known Nb-Zr-Ti alloy and Nb-Ti-Ta alloy which plastic processing is relatively easy. Critical magnetic field of these alloy superconductors is 100-120 KOe at liquid helium fernperature Q 1210 and lower than that of compound superconductor such as Nb Sn and V Ga, i.e., 200-220 KOe. However, these compound superconductors are poor in processability and it is difficult to fabricate the compound superconductor into wire. Therefore, alloy superconductor is practically used for commercial purpose at the present time.

The present invention is relevant to an alloy superconductor which gives critical magnetic field higher than that of compound superconductors. Furthermore, critical temperature of alloy of the present invention is higher than that of prior art superconductive alloys such as V-Hf-Zr, V-Hf-Cr, V-Hf-Ta, V-Hf-Mo and V- Hf-W.

Hereinafter the composition of alloy is shown by atomic percent.

SUMMARY OF THE INVENTION According to the present invention, there is provided an alloy for superconductive magnet comprising a ternary alloy of V-Hf-Nb wherein contents of V, Hf and Nb are 30-90 percent, 5-65 percent, and less than 40 percent, respectively.

An object of the present invention is to provide a superconductive alloy having a critical magnetic field higher than superconductors of compound type.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 represents critical temperature isotherms of the V-Hf-Nb ternary alloy according to the present invention;

FIG. 2 represents isocritical magnetic field (the same critical magnetic field) of V-Hf-Nb ternary alloy according to the present invention; and

FIG. 3 shows diagrammatically a process for producing a tape of an alloy of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT general, a material showing a critical current density of higher than l i I O A/cm at a magnetic field of0TCO is excellent from practical point of view. According to the present invention, a critical current density as high as 2.8 Z l0 A/crrF at jfiiOe c an be 6156mm;

In view of the foregoing, practically excellent superconductor according to the present invention may be produced by some manufacturing and processing methods selected taking into consideration processability of a material itself and effect of a processing method on the superconductive properties.

An alloy of the present invention in a certain composition region may be produced by conventional means such as melting, heat treatment and plastic processing.

According to a manufacturing method, component metals corresponding to a composition are mixed and melted in an arc melting furnace followed by molding to procude a mold material. The resulting mold material has two-phase system produced by formation of a superconductive phase of poor processability which is not suitable for direct plastic processing. Therefore, this material is subjected to melting treatment at 950-I400C. Then the mold material is fabricated into thin wiresor tapes of desirable size followed by heat treatment at 300-900C to produce a phase of excellent superconductive characteristics.

. An alloy of the present invention insideof isotherm 3 indicated by cross oblique lines in FIG. 1 is relatively poor in plastic processability. Therefore, it is necessary to wrap the molding material with a stainless steel sheath and extrude at about l,200C.

There may be employed a powder metallurgical method which comprises by mixing sufficiently component metal powders at a desirable mixing ratio, shaping in a mold and sintering at 800-l,400C.

Particle size of metal powder in the above mentioned procedure is not particularly limited, but particle size used in usual powder metallurgy may be employed. The sintering temperature of 800l,400C is suitable for converting a sintered matter to a multi-component alloy of easy plastic processability. The resulting sintered matter thus treated is fabricated into, for example, a thin wire of desirable size and shape by plastic processing.

According to another manufacturing method, a binary alloy of easy processing such as V-Nb, V-Hf and Hf-Nb, is overlaid on another simple substance metal, or the latter simple substance metal is fitted into atube or cylinder of the former binary alloy or a hole in a billet. The resulting composite is subjected to plastic processing to form a thin wire or tape of desirable size. In the above mentioned processforfabricating the composite, the binary alloy and the simple substance metal may be arranged in an opposite manner. In the above mentioned wire or tape, the binary alloy and the simple substance metal closely contact each other at the boundary. Then the wire or tape is subjected to thermal diffusion treatment to produce at the boundary a superconductive alloy material containing a uniform and continuous ternary alloy diffusion layer.

The thermal diffusion treatment is effected by heating the composite at 850-l,300C in an inert atmosphere or vacuum for more than several minutes. Thus there is formed a diffusion layer of a ternary alloy having a composition within the isotherm 3 indicated by cross oblique lines.

The present inventors have found that the composition of the diffusion layer is affected by the heat treating temperature and the composition of the binary alloy such as V-Nb, Hf-Nb and the like.

The above mentioned various processing methods may be applied to an alloy having a composition within the isotherm 1. Further, the following processing methods may be also used, that is, a processing method comprising depositing simultaneously V, l-If and Nb on a surface of a base material by vacuum evaporation, a processing method comprising melting and applying the ternary alloy to a base material by plasma jet, and a vapor phase reducing method comprising reducing simultaneously halides of V, l-lf and Nb with hydrogen to deposit the metals on a base material. In each of the above-mentioned methods, the base material may be one simple substance metal which is one component of the ternary alloy and further may be a material incapable of reacting with any of metal components of the ternary alloy such as stainless steel and quartz glass.

The following examples are given for illustrating the present invention, but should not be constructed as limitation thereto.

EXAMPLE 1 V, Hf and Nb were mixed and arc-melted in an argon atmosphere by using a water-cooled copper crucible to form an ingot. Both ends of a bar-like sample cut out from the ingot were copper-plated and then lead wires were soldered thereto. Thus there was obtained a sample for determining critical temperature and critical magnetic field. The resulting sample was placed in a sample room, temperature distribution in which was uniform. Te critical temperature was determined by measuring simultaneously the electric resistance and the temperature change of the sample. The temperature was adjusted by soaking the sample in liquid helium and taking out gradually the sample from the liquid surface.

The critical temperature was defined as a temperature at which the electric resistance of the sample ternary alloy becomes a half of the value of electric resistance at normal conductive state. As the result of the measurement, there were obtained triangular coordinates showing the composition of the ternary alloy and the critical temperature as illustrated in FIG. 1. The V- 'I-If-Nb alloy having composition within isotherms and in FIG. 2. The region within isocritical magnetic field curve 4 indicated by oblique lines and cross oblique;

' lines corresponds to a range of V -90%, Hf 565% and Nb less than percent and alloy in this region a critical magnetic field of higher than 100 KOe shows at 4.2K

Critical magnetic field of superconductive alloy of Nb system widely used at the present time g 1' 100-120 KOe and therefore, if a critical magnetic field ofmpercondllctive material is higher than 100 K06, I such superconductive material practically valuable as that for generating high magnetic field. Furthermore,

the region within isocritical magnetic field curve 6 as indicated by cross oblique lines in FIG. 2 shows critical ifiagnetlc field of higher than 250 KOe/This critical magnetic field is far higher than that of Nb Sn or V Ga having the highest critical magnetic field as high as "210-220 KOe. Thus, the superconductive material of the present invention is an excellent one for high magnetic field.

EXAMPLE 2 From V-SNb alloy produced by electron beam melting, there was cut out a hollw cylinder 2 of 5 mm. in inner diameter, 10 mm. in outer diameter and 100 mm. long, as shown in FIG. 3a. A hafnium rod 1 of 100 mm. long in FIG. 3a was fitted into hollow cylinder 2 to form a composite (FIG. 3b) followed by cold rolling to produce a tape of3 mm. wide and 0.2 mm. thick (FIG. 3c).

; The resulting tape is a composite of Hf and V-5Nb alloy which are closely contacted each other. The resulting composite tape was heat-treated at 950C or 1,000C in vacuum of 10 mml-lg to produce four kinds of su- 'perconductor having a ternary alloy layer 3 formed by {heat diffusion at the interface (FIG. 311).

I Properties of these superconductors are as shown in Table 1 below.

Composition of the heat diffusion layer is analyzed by an X-ray microanalyzer. Critical current density is determined by applying a constant external magnetic field of 30 KOe to the sample in liquid helium in a direction rectangular to the sample current. As is clear from 5 Table 1, the new superconductive material of the present invention has a very high critical current density and can be practically used as superconductive magnet material.

Tablet Heat Composition of Critical Critical Sample treatment diffusion layer current temperature condition V l-lf Nb density(A/cm K A 950CX20 hrs. 70 28 2 2.8 l0 9.8 B 950C 50 hrs. 68 29 3 2.3Xl0 9.9 C l,000C l0 hrs. 67 30 3 2.2Xl0 l0.l D 1,000CX20 hrs. 66 30 4 2.0 I0 [0.3

critical magnetic field. The external magnetic field was A magnetic field of higher than KOe can be easily produced, and furthermore, a magnetic field of higher than 200 KOe which can not be produced by conven tional superconductive material can be generated by using the superconductive material of the present invention.

I claim:

1. Alloy for superconductive magnet comprising a ternary alloy of V-I-If-Nb wherein contents of V, l-If and Nbare 30-90 atomic percent, 5-65 atomic percent,

and less than 40 atomic percent, respectively. 

